Re: ATL COM library - BSTR question

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.atl

Date:

Wed, 2 Jan 2008 21:46:20 -0500

Message-ID:

<#$#OTLbTIHA.280@TK2MSFTNGP03.phx.gbl>

"2b|!2b==?" <user@domain.invalid> wrote in message
news:n4qdnUjv-dMz1OHanZ2dnUVZ8s-qnZ2d@bt.com

I have a wrapper COM object that makes calls to a C++ object.

I have two methods on the C++ class like this:

std::string foo();
void foobar(const std::string&);

I have two questions:

1). how do I convert from BSTR to std::string (and back to BSTR)

Realize that BSTR holds Unicode characters, while std::string holds
narrow characters. Which encoding do you plan to use in your std::string
representation?

If you are sure the string will only ever contain 7-bit ASCII, something
like this should work:

BSTR b;
string s = COLE2A(b);

BSTR b2 = CComBSTR(s.c_str()).Detach();

2). If I have a COM method that returns a BSTR, presumably, I use
SysAllocString() to create the BSTR. However, the client consumer (in
this case VB) does not call SysFreeString (AFAIK) - surely this must
cause memory to leak ?

It does too call SysFreeString. In case of VB, the call is hidden in VB
runtime.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925